(1) Field of the Invention
The present invention relates to a paste for electron emission sources and an electron emission source using the paste.
(2) Description of Related Art
A carbon nanotube has excellent physical and chemical durability and has a sharp-pointed tip shape and is therefore suitable to an electron emission material. This is why electron emission sources using a carbon nanotube are being researched and developed in the fields of displays and luminaries.
The structure configured to obtain emission in displays, luminaries and the like by an electron emission source using a carbon nanotube is as follows. First, a high electric field is applied by a gate electrode and the like to an electron emission source including a carbon nanotube formed on a cathode substrate in a vacuum-sealed container. Then, the electric field is concentrated at a sharp-pointed tip of the carbon nanotube. When the intensity of the electric field exceeds a fixed threshold value, electrons are emitted by a tunnel phenomenon. The electrons emitted in this manner collide with a fluorescent layer formed on an anode substrate to obtain emission.
Among methods of producing an electron emission source using a carbon nanotube, there is a method in which a carbon nanotube is made into paste, which is then applied to a cathode substrate. This method involves a step of forming a coating film of a carbon nanotube-containing paste on a cathode electrode by screen printing, a step of removing organic materials which are the cause of deteriorating the degree of vacuum by heat treatment, from the coating film of the carbon nanotube-containing paste, and a step of performing activation treatment such as the tape peeling method and laser radiation method to the heat-treated surface of an electron emission source. As the paste material of the carbon nanotube used in this method, carbon nanotube-containing pastes containing a glass powder (see, for example, Japanese Unexamined Patent Publication No. 2007-115675), a carbonate (see, for example, Japanese Unexamined Patent Publication No. 2003-242898) or a metal carbonate (see, for example, Japanese Published Patent Publication No. 2008-500933) are known.
In the meantime, the activation treatment among the above steps is carried out to expose a carbon nanotube from the electron emission surface by napping treatment or the like to obtain good electron emission characteristics. However, if the step of activation treatment can be omitted, this can largely contribute to further reduction in cost.
As a method used to obtain good electron emission characteristics without performing the napping treatment, an electron emission source is proposed which comprises an electron emission material including a carbon nanotube, a cathode electrode and gate electrode that impart an electric field to the electron emission material, and a porous member including continuous pores between the cathode electrode and gate electrode wherein the porous member contains electron emission material and the tip part of the electron emission material projects from a pore wall of the porous member (see, for example, Japanese Unexamined Patent Publication No. 2004-87304). This electron emission source is obtained by forming voids in a region where plastic particles exist, thereby forming a continuous hole in a process in which the plastic particles such as methyl polymethacrylate are mixed in a carbon nanotube-containing paste to remove organic materials from the carbon nanotube-containing paste coating film by heat treatment. Since a carbon nanotube projects from a pore wall, it is unnecessary to carry out activation treatment. In this method, it is easy to increase the exposure amount of the tip part of the electron emission material and to improve the uniformity of exposure, enabling electron emission characteristics to be uniformed.